1. Field of the Invention
The present invention relates to an optical fiber photoelectric sensor unit which can be linked contiguously and closely with other units via an attachment rail such as a DIN rail, and more specifically relates to an optical fiber photoelectric sensor unit which can be preferably linked with a large number of other units in a small area.
2. Description of the Prior Art
There is an already known optical fiber photoelectric sensor unit which can be linked with a large number of other units via a DIN rail and which includes one set of light-emitting and light-receiving fibers, one set of light-emitting and light-receiving circuits, and one output line (See Patent Document 1).
There is another already known optical photoelectric sensor unit in which a sensing system circuit that realizes an intended sensing function by being linked with the fiber head; a first optical communication system circuit that includes a light-emitting and light-receiving elements to perform a bi-directional optical communication with the adjacent sensor unit on one side when plural sensor units are contiguously linked; and a second optical communication system circuit that includes a light-emitting and light-receiving elements to perform a bi-directional optical communication with the adjacent sensor unit on the other side when plural sensor units are contiguously linked, and these three circuits are accommodated in a housing which enables the photoelectric sensor unit to be linked with a large number of other units via a DIN rail, whereby a bi-directional optical communication can be conducted with the adjacent sensor units on both sides in the condition where the photoelectric sensor unit is contiguously linked with other units (See Patent Document 2).
There is further another already known optical fiber photoelectric sensor unit which tries the handshake processing with its adjacent sensor units on both sides when linked with other units by means of the first and second communication system circuits to learn its own position in the plural sensor units linked together, assigns the learned inherent address, generates the timing of the sensing action inherent to its position and drives the sensing system circuits according to the timing of the sensing action to attain its sensing action. Meanwhile, the sensor unit has a data selection/transfer function to transfer the data received from the adjacent sensor unit on one side to the adjacent sensor unit on the other side excluding the data that are addressed to its own unit during the intervals of sensing actions and also has another function to carry out the commands included in the data addressed to its own unit (See Patent Document 3).
There is further another already known optical fiber photoelectric sensor unit which is provided with plural detection channels. The front surface of the sensor unit includes a pair of vertically aligned light-emitting and light-receiving optical fiber inlets corresponding to one detection channel, and such a pair of light-emitting and light-receiving optical fiber inlets are laterally arranged the same number as the detection channels (Patent Document 4).
[Patent Document 1]
Japanese Laid-open Patent Application No. 2002-279871
[Patent Document 2]
International Publication No. 01/31607
[Patent Document 3]
Japanese Laid-open Patent Application No. 2001-222786
[Patent Document 4]
Japanese Laid-open Patent Application No. 07-301733
As controls get more complex and more advanced in industrial field in recent years, there is a growing demand for controlling a number of objects to be detected by a single control device. In the case where a number of objects to be detected are arranged densely, optical fiber photoelectric sensor units are often adopted because of their small sensor head and usability. Above all, an optical fiber photoelectric sensor unit which can be linked with a large number of other units contiguously and closely via a DIN rail is preferable because a large number of sensor units can be installed in a small space.
However, the conventional optical fiber photoelectric sensor units disclosed in Patent Documents 1 to 3 can handle one channel's worth of detecting operation. Therefore, when there are plural objects to be detected such as 8 channels (8 sites), 16 channels (16 sites) or 32 channels (32 sites), it is necessary to arrange as many optical fiber photoelectric sensor units as the channels. Concerning the width and thickness of the sensor unit in the direction to be linked with other units, as the result of manufacturers' efforts to reduce the dimensions, the width has been reduced to 10 mm or so. However, since there are limits to their efforts to reduce the dimensions, as the number of channels increases, the length of a string of sensor units linked on the DIN rail becomes non-negligible. In particular, when the sensor units are forced to be installed inside a control device such as a machine tool, there are more constraints in space than the case where sensor units are installed inside a general control panel.
Since sensor units are independent from channel to channel as products, it becomes costly to use a number of them. It is possible to realize cost reduction by handling a number of detection channels by a single product, although a large case is necessary for the sensor units. However, different users require different numbers of channels, and satisfying every user would require various types of sensor units having different number of channels, which is far from achieving sufficient cost reduction. As another problem, when a multi-channel sensor unit is produced, it is not apparent what structural consideration should be taken in terms of performance such as output response, the function of being linked with other optical fiber photoelectric sensor units, and usability. As further another problem, arranging the optical fiber inlets of plural detection channels in the lateral direction as in the optical fiber photoelectric sensor units disclosed in Patent Document 4 cannot obtain the effects to save space from the multi-channel structure.